Television communication systems presently employ vestigial sideband (hereinafter referred to as VSB), or asymmetric-sideband, modulation wherein a portion of one sideband (usually the lower sideband) is largely suppressed. A typical VSB television channel has the picture carrier located somewhere in the VHF or UHF band, depending upon the channel assignment, with a 25 KHz FM modulated sound carrier displaced on the unsuppressed sideband side of the picture carrier by 4.5 MHz. One exemplary type of television communication system is the cable television network, wherein multi-channel television signals are transmitted from the system headend along a network of distribution points each serving a plurality of subscribers, with coupling between stations being effected over cable conductor links. In order to avoid signal degradation, some means must be provided to maintain required signal strength between stations. Unfortunately, the simple use of repeaters has not proved satisfactory, due to substantial repeater distortion which renders the quality of transmitted analog signals unacceptable.
To obviate this drawback, digital conversion schemes have been proposed wherein the original VSB television signals are demodulated at an originating station, converted into digital format, and then transmitted to a distribution point. At the distribution point, the received digital signals may then be converted back into analog format and then modulated by a VSB modulator, so that the analog signals will be compatable with the subscribers television receiver circuits. A significant drawback to this digital approach is the need for VSB demodulation and modulation circuitry at each station along the communication network for each channel handled by the network in order to bring the sampling rate of the television signals down to a value that can be handled by available analog/digital conversion equipment. VSB modulation/demodulation circuitry is an expensive and complex part of the equipment required at each station, and where a large number of channels are to be served, even the apparently improved digital approach to maintaining signal quality while expanding a service area is subject to economic restrictions.